In recent years, as one of chemical field-effect transistors (Chem-FETs), an ion-sensitive field-effect transistor (ISFET) configured to detect a change in a chemical substance such as a hydrogen ion or the like now receives attention. Further, recently, a time width modulation type ISFET configured to apply a time-varying signal such as a ramp wave or the like to a dual gate to thereby output a chemical state as a pulse width is proposed.